Carbohydrates are not your enemy.
Carbohydrates are not your enemy
Over the last 25 years there has been a big push in diet trends way from the high carbohydrate/ low fat doctrine of the 60’s, 70’s and 80’s to a high fat/ low carb approach favoured by popular diets like Atkins. The reasoning behind these diets are based on the perceived evils of a hormone called insulin.
The proponents of these diets claim that reducing insulin spikes prevents fat gain and to do so, we have to minimise or eliminate carbohydrates or only eat low GI foods. They completely ignore the masses of evidence from clinical trials that show fat loss is a result of a calorie deficit, regardless of meal composition.
I mentioned low GI foods and you might be wondering what I mean by that.
GI means Glycaemic Index and is a measure of how quickly foods can in increase blood sugar levels.
Table sugar has a score of 100 and is used as the standard by which everything else is measured. The more complex the food source is, the lower it’s score.
To explain further, you need to understand the structures of carbohydrates (also called saccharides.)
Carbohydrates are made from chains of glucose molecules, there are
1. Monosaccharides (single glucose molecule), Glucose, Fructose and Galactose
2. Disaccharides (two molecules), Sucrose, Lactose and Maltose
3. Oligosaccharides (3 molecules), Fructo-oligosaccharides (can cause bloating, often mistakenly diagnosed as gluten intolerance)
4. Polysaccharides (multiple molecules), Starch, Cellulose (the indigestible skin of sweetcorn), Glycogen (how glucose is stored in the body as a primary fuel source.)
A glucose molecule is an arrangement of 6 carbon, 12 hydrogen and 6 oxygen atoms C6H12O6 and looks like this,
Different types of saccharides have different structures based around the glucose molecule which determines how quickly they are broken down in the intestines and therefore how fast they release their energy into the blood stream. The more complex the arrangement of glucose molecules, the longer it takes to break down and therefore, the lower the GI score.
It is this speed of breakdown that determines the insulin response of our bodies, a rapid increase in blood sugar leads to a more pronounced increase in Insulin and this forms the premise of low GI or low carbohydrate diets.
So, what is insulin and what does it do?
Simply put, Insulin is a hormone secreted by our pancreas. With the exception of type 1 diabetics, we all have a base level of insulin that keeps our blood sugar in the range of 4.0-6.0 mmol/l and as a response to elevated blood sugar it increases to signal the body to remove excess glucose and return our blood sugar back to normal levels.
Where the books get it wrong is, they call insulin the fat storage hormone. This is true in part, but it does so much more.
Yes, Insulin does signal fat cells to take on glucose, but they aren’t the only cells that can do this and how much of it that gets stored as fat is entirely dependent on whether or not the rest of the body is at its capacity for glycogen storage. Insulin partitions glucose into the liver, the muscles and a whole number of other tissue types as well as fat cells.
What else happens when Insulin is elevated?
Our fat cells release energy for the body to use via a process called lipolysis, this energy can either be oxidised (burned off) or recycled back into the liver and then the fat cells, when Insulin is elevated it tells the fat cells to switch off the lipolysis function. Fortunately for us, this only lasts as along as insulin is elevated, once it drops back to base line, lipolysis resumes. At the same time that lipolysis switches off, fat cells can become more sensitive to something called the GLUT4 protein, this is one of 13 glucose transport proteins (GLUT) that work with differing sensitivities to blood sugar levels to move glucose to different types of cell in the body. Now, even though some glucose will be partitioned to the fat cells for storage, this is compensated for by lipolysis, and unless there is an excess of glucose, more energy from fat will be burned off than can be replaced with glucose, leading to a reduction in fat mass.
When blood sugar rises and insulin is elevated, it partitions some of that glucose to the liver. The liver can turn glucose into glycogen which is stored until needed (when blood sugar drops too low, a hormone called glucagon signals the liver to release energy back into the blood stream.) However, if there is an excess of glucose, the liver metabolises it into fatty acids which can then be stored as fat. (It is important to note that carbohydrates aren’t the only nutrient that can signal the increase of insulin, protein is extremely good at doing this too, particularly if the amino acid leucine is present in a large amount, the only difference here is that there is less blood sugar to deal with.)
Insulin also triggers muscle cell uptake of glucose, by allowing the cell to become sensitive to the GLUT4 protein, the effectiveness depends on how empty the muscles are to start with and whether or not they are trained. The muscles can take on 2% glycogen per kg as opposed to the liver which can hold 10% per kg. Glycogen is great for the muscles as it’s a more readily available fuel source than fatty acids and can be used without the presence of oxygen, making it the preferred fuel source for anaerobic exercise and weight training. These types of exercise deplete our muscle cell glycogen and increase the sensitivity of the muscles to take on more after feeding. Think of the muscle as a sponge, a wet sponge (fully saturated muscle cell) will not take on any more water, but a dry sponge (depleted muscle cell) will absorb a large amount.
Despite what you may have heard, elevated insulin actually reduces appetite, this ties in with the hormone Leptin in helping manage our hunger (more on Leptin later.)
Insulin is the main driving force of muscle protein synthesis, as it signals uptake of glucose by the liver and muscles and working with the amino acid Leucine, it triggers the repair of muscle cells that were damaged during training. (This is a very simplified version of what happens.) It’s so effective at promoting muscle protein synthesis that bodybuilders will actually inject insulin to promote increased muscle growth, hardly something you would do in a sport where extremely low body fat levels are a prerequisite if insulin did in fact make you fat.
But I lost weight when I reduced my carbohydrate intake.
Excellent, but it wasn’t the reduction of carbohydrates that caused the weightloss, it was the reduced calorie intake that came about from eating less carbs and sugar, particularly where that sugar also came with a healthy dose of fat.
Let’s take a Mars Bar for example, a standard sized bar that weighs 51 grams, contains,
35.3g of carbohyrates, which equates to 141.2 calories
8.5 grams of fat, which equates to 76.5 calories
2.2 grams of protein, which is 8.8 calories
When you lower your sugar intake by not eating that Mars Bar you might otherwise have enjoyed, you are reducing your intake by 226.5 calories, 85.3 of which, come from the other macronutrients that come with all that sugar.
But I’m Fat adapted.
I hear this one a lot, when people talk about being on very low carbohydrate diets. Sorry, but you’re not and here is why.
When you stop consuming a fuel source, eventually, your natural stores of said fuel will get used up, then your body can only burn what is available to it, so, if you only eat high fat diets, you will burn fat for fuel, this doesn’t mean you are burning more stored fat than those who consume carbohydrates, it means you are burning more ingested fat for fuel, big difference.
You are no more fat adapted than someone can be carb adapted who follows a low to zero fat diet.
How many grams of carbohydrates can we store?
As mentioned above, glucose gets metabolised in the liver and turned into glycogen, excess glucose is metabolised into fatty acids which are then stored as fat. The key word here is EXCESS. We know that skeletal muscle can store 2% of its weight as glycogen, the liver can store 10%. In real numbers this could be anywhere between 300-500 grams stored in our muscle and 100-150 grams stored in the liver. Unfortunately, our fat cells have an almost infinite storage capacity for fatty acids and when the liver and muscle cells are full, the only place we can put excess glucose is fat cells.
When we are active, we use a lot of fuel, training with weights, running or working in manual jobs all contribute to us using the glycogen that is stored within for fuel. If we are sedentary or work desk jobs/ sit at the wheel of a car all day, we use much less fuel. Low carb diets are better prescribed to people who fall into the latter category. They burn less glycogen, therefore don’t need to consume as many grams of carbohydrates as someone who burns lots. Think of it like a car, do you put more fuel in when you aren’t using it?
Low carb diets that are prescribed to obese clients are usually at 50 g or less, these are also the recommendations found in a lot of low carb diet plans. Unfortunately, this one size fits all approach doesn’t account for lifestyle, exercise habits, work activity and non-exercise activity levels, so what works for the morbidly obese patient that can barely move is going to be a disaster for someone in healthy rages that has a highly active lifestyle.
The negative effects of low carbohydrate consumption
I want to briefly cover some effects of low carbohydrate intake on thyroid function.
The thyroid is the master control switch for our resting metabolic rate, and it is vital that we keep it functioning properly. To do so we need an appropriate amount of carbohydrates in our diet, too few and the thyroid reduces its output of the T4 hormone, that converts in the liver to T3, T3 is the active component that controls energy expenditure and glucose metabolism in the body.
When we reduce carbohydrate intake, it suppresses T3 production and can actually increase levels of reverse T3, reverse T3 can block or inhibit the effect of T3 on the body causing a slowing of the base metabolic rate and give you that cold sluggish feeling.
Other lesser known effects of low carbohydrate diets include,
· An irregular or stopped menstrual cycle,
· Decreased fertility,
· Hypoglycaemia and blood sugar swings,
· An increase in abdominal fat due to a rise in the stress hormone cortisol,
· Loss of bone density
· Other chronic problems.
As you can see, the advice to drop to very low carbohydrate levels is often given out without thought for the consequences and should not be prescribed by anyone except in the case of a clinical intervention where obesity is at a life threatening level.